Build Catch3 as C++17

C++17 is still the widest common target, and a library built on it stays
usable from C++17 and every later standard, while C++20 would have left
out many users.

Concepts become enable_if on named traits in Detail/TypeTraits.hpp, which
also replaces std::remove_cvref_t and std::identity. std::span becomes
std::vector references, std::bit_cast becomes static_cast and memcpy,
template lambdas become helper templates, and std::erase_if, contains,
starts_with and ends_with have their C++17 forms. Random::Between no
longer uses a lambda over a constexpr local, which MSVC rejects outside
/permissive-, so the headers work under its default mode too.

Tests give up designated initializers, which MSVC refuses in C++17. CI
builds the matrix in C++17 and C++20, since the headers promise both.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/Progmasoft/ChoiceShrinker.cpp b/src/Progmasoft/ChoiceShrinker.cpp
index c1aac19c..b9b5a47d 100644
--- a/src/Progmasoft/ChoiceShrinker.cpp
+++ b/src/Progmasoft/ChoiceShrinker.cpp
@@ -14,8 +14,8 @@ namespace Progmasoft::Catch3::Detail
 {
 
     bool
-    IsSimpler(std::span<const std::uint64_t> candidate,
-              std::span<const std::uint64_t> current) noexcept
+    IsSimpler(const std::vector<std::uint64_t> &candidate,
+              const std::vector<std::uint64_t> &current) noexcept
     {
         if (candidate.size() != current.size())
         {
@@ -299,7 +299,7 @@ namespace Progmasoft::Catch3::Detail
     }
 
     std::string
-    EncodeChoices(std::size_t size, std::span<const std::uint64_t> choices)
+    EncodeChoices(std::size_t size, const std::vector<std::uint64_t> &choices)
     {
         // c3.<size>.<choice>-<choice>-... with each number in base 36: short
         // enough to paste from a CI log, and only characters that survive
@@ -329,7 +329,7 @@ namespace Progmasoft::Catch3::Detail
     std::optional<DecodedChoices>
     DecodeChoices(std::string_view token)
     {
-        if (!token.starts_with(kTokenPrefix))
+        if (token.substr(0, kTokenPrefix.size()) != kTokenPrefix)
         {
             return std::nullopt;
         }